1. Field of the Invention
This invention relates generally to thrusters and, more particularly, to underwater thrusters for submarine vessels.
2. Description of the Related Art
Underwater drilling, research, searches, investigations, and similar operations commonly are performed using submarine vessels configured to travel thousands of feet below sea level. These submarine vessels include personnel operated vehicles (POVs) and remotely operated vehicles (ROVs). Both types of vehicles are propelled through the water using a propulsion system.
Modern underwater propulsion systems include a thruster having a magnetic flux generating stator, a shaftless propellant rotor, electrical conductors to supply electrical current to the thruster, and an electronic controller to regulate the electric current. The stator includes a plurality of magnetizable pole pieces, each associated with windings of conductive wires electrically connected to a power supply via the controller. The rotor includes a propeller ring containing a plurality of permanent magnets to be torqued by the magnetic flux from the stator pole pieces. The rotor further includes a plurality of propeller blades projecting inwardly from the propeller ring and a plurality of bearing assemblies connected to the propeller ring. The bearing assemblies are sealed and oil-filled, to lubricate the contact surfaces. Control of the rotor is accomplished by controlling the electrical current supplied to the stator windings. Nozzles are located on opposite sides of the rotor, surrounding the propeller blades, to improve the thruster""s operating efficiency. An exemplary underwater propulsion system is described in U.S. Pat. No. 5,306,183, and an exemplary bearing assembly is described in U.S. Pat. No. 5,529,399.
Underwater propulsion systems of this type have several drawbacks. For example, most underwater propulsion systems have more than 100 moving parts, which can require substantial maintenance and service operations. In addition, underwater propulsion systems generally have sealed, oil-filled bearing assemblies that are vulnerable to seawater intrusion.
It should, therefore, be appreciated that there is a need for an underwater propulsion system or thruster that requires fewer moving parts and that eliminates the need for bearing assemblies having sealed, oil-filled bearing assemblies vulnerable to sea water intrusion. The present invention fulfills these and other needs.
The present invention is embodied in an improved underwater thruster having fewer moving parts than previous thrusters and eliminating the need for sealed bearing assemblies vulnerable to sea water intrusion. In particular, the thruster of the present invention includes a stator assembly having a ring-shaped stator body that encapsulates a plurality of coils and further having two ring-shaped stator bearing assemblies located on opposite sides of the stator body, encircling a circular opening. Each of the stator bearing assemblies has a journal bearing surface and a thrust bearing surface. The thruster further includes a rotor assembly having a ring-shaped rotor body that encapsulates a plurality of rotor magnets and further includes two ring-shaped rotor bearings, located on opposite sides of the ring-shaped body. Each of the rotor bearings has both a journal bearing surface and a thrust bearing surface for bearing engagement with the respective journal and thrust surfaces of the one of the two stator bearings. The rotor assembly further includes a plurality of propeller blades secured to the rotor body and arranged to project inwardly therefrom. A controller supplies electrical current to the coils of the stator assembly, to create a controlled electromagnetic field within the circular opening of the stator assembly, which interacts with the magnetic field of the rotor magnets, to cause the rotor assembly to rotate about a central axis.
In more detailed features of the invention, the thruster further includes a pump that directs filtered water past the stator bearings and the rotor bearings, to lubricate and cool the bearings and to cool the coils of the stator assembly. The pump preferably is a centrifugal pump that includes a plurality of radially oriented grooves formed in a planar wall of each of the two rotor bearings, for slinging water radially outwardly when the rotor assembly is rotated about the central axis. The pump further includes a plurality of holes formed through the planar wall of each of the two rotor bearings, each such hole being aligned with a separate one of the plurality of grooves, for directing water to the grooves. The pump provides suction that draws unfiltered sea water through a filter located adjacent to a water inlet formed in the stator body. A flapper valve is located downstream of the pump, for preventing the intrusion of unfiltered sea water into the region of the stator bearings and rotor bearings when the rotor assembly is not rotating.
In other more detailed features of the invention, the stator bearing assembly includes a plurality of arc-shaped segmental bearings positioned end-to-end to form a ring shape. Each segmental bearing includes a journal bearing segment that defines the journal bearing surface and a thrust bearing segment that defines the thrust bearing surface. Further, the thrust bearing segment of each segmental bearing includes a post that projects radially outward from a mid-portion of the journal bearing segment and two arms cantilevered laterally from the post. A radial recess is formed in the portion of the thrust bearing surface defined by each cantilevered arm of each segmental bearing. Each of the plurality of arc-shaped segmental bearings is formed of a plastic material, as a unitary component.
Other features and advantages of the present invention will become apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.